circulatory system

Main Functions of the Circulatory System

Carries oxygen, nutrients, and hormones to all cells; removes waste, protects against blood loss, and regulates body temperature.

Open Circulatory System

Blood flows freely in body cavities; cells are bathed in blood, seen in insects and mollusks.

Closed Circulatory System

Blood stays inside vessels and is separated from cell fluid; seen in worms, squids, and vertebrates including humans.

Components of Blood

Blood consists of plasma (55%) and formed elements (45%) such as red blood cells, white blood cells, and platelets.

Plasma

The liquid part of blood, consisting of ~90% water and ~10% proteins, nutrients, and ions.

Red Blood Cells (RBCs)

Erythrocytes that carry oxygen to cells and remove carbon dioxide, made in bone marrow and contain hemoglobin.

White Blood Cells (WBCs)

Leukocytes that defend the body from infections, made in bone marrow and have nuclei.

Platelets

Thrombocytes that help form blood clots, originating from larger cells in bone marrow.

Blood Clotting Process

Platelets stick to torn vessel edges, release chemicals to trigger fibrinogen into fibrin, forming a mesh that traps RBCs.

Capillaries

Smallest blood vessels where gas and nutrient exchange occurs, with walls only one cell thick.

Venules

Small veins that collect blood from capillaries and carry it to larger veins.

Veins

Thin-walled vessels that carry deoxygenated blood back to the heart, except for pulmonary veins which carry oxygenated blood.

Heart Chambers

Four chambers of the heart: Right Atrium, Right Ventricle, Left Atrium, and Left Ventricle, each with specific blood flow functions.

Cardiac Cycle

A complete heartbeat consisting of two main phases: Diastole (relaxation and filling) and Systole (contraction and pumping).

Blood Pressure

The pressure of blood pushing against artery walls, with systolic pressure measured during ventricular contraction and diastolic during relaxation.